SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey March 12, 1998 Weekly Earthquake Report for Southern California ------------------------------------------------ March 5 - 11, 1998 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U. S. Geological Survey California Institute of Technology For further information, please contact the authors, or the Caltech Public Relations Office at 626-395-6327. For daily updates, call our Earthquake Information Hotline: 626-395-6977. -------------------------------- ****************************************************************** As many of you know by now, the U.S. Geological Survey in Menlo Park, the office which originates the Northern California Earthquake Report, has discontinued their Weekly Report. We plan to follow their initiative. As of late March 1998, we will be replacing our weekly 'treeware' product with a Web site, which will include the same map, table, and commentary as the current Weekly Report, plus other features. The Web page will be updated more often than once per week. Commentary on current notable quakes can be found on http://www.trinet.org/ and our day-to-day commentary will soon be there as well. After March 26, There will be no paper copy or usenet distribution. We hope we have giving our Users sufficient notice to obtain World Wide Web access for themselves. At minimum, most public libraries now provide Web access, along with the capability to print copies of Web pages. ****************************************************************** This week's Report covers the time period from midnight Thursday morning, March 5, Universal Time (ie. UTC), to midnight Wednesday night, March 11, Universal Time. In local time, the period of coverage is from 4 p.m., March 4, Pacific Standard Time, to 4 p.m., March 11, Pacific Standard Time. We have processed 797 earthquakes for the seven-day period covered, and we have about 200 more small ones to go. We certainly did not have a quiet week this week! The largest earthquake in our region since March 1997 occurred last Thursday night (March 5) at 9:47 pm in the southern Owens Valley, near the town of Little Lake, near the Coso geothermal area. It had a magnitude of ML5.2 and was located just 2 km east of a ML5.3 on Thanksgiving 1996. A second M5+ quake (ML5.0) occurred the next day, at 4:36 pm on Friday. Interestingly, the ML5.0 had considerably fewer aftershocks than the ML5.2 did. The Owens Valley is an extensional regime, but most of the focal mechanisms are strike-slip, including this week's events. The aftershocks of Thursday's quake strike northeast, suggesting that the causative fault is left-lateral strike-slip on the northeast-strikign plane. The aftershocks of Friday's quake follow the same trend. Although the Little Lake quakes were felt in the China Lake and Ridgecrest areas, the did not cause much public stir. A smaller quake (ML4.5) did that in the early hours Tuesday. That quake occurred in the Crafton Hills, near Redlands, and woke most people in the Inland Empire. It was widely felt, as far away as Thousand Oaks and Palm Springs. The strongest shaking recorded by us was 10% of the force of gravity, in Riverside. By contrast to the Little Lake quakes, the Crafton Hills quake had produced a total of four aftershocks, as of 4 pm on Wednesday, the largest of which was M2.0. The Crafton Hills quake was located near the intersection of the San Jacinto Fault and the Crafton Hills Fault. The focal mechanism of the quake indicates normal faulting (tension in the crust), with a strike consistent with the Crafton Hills Fault. Because the quake occurred at 14 km depth (9 miles), however, and we are not sure of the location of the fault at that depth, we are cautious about associating the quake with that or any particular fault. The Crafton Hills region is historically one of the most active in southern California. The largest quake in that area was a ML4.8 at almost the same location, and also at 15 km depth, in October 1985. The 1985 earthquake, unlike this one, was a strike-slip earthquake, probably on the San Jacinto fault. Table 1 lists the quakes this week that were M2.0 or larger in the central part of the coverage area. Times are local times; if you want Greenwich Mean Time, add 7 hrs to the Pacific Daylight Time or 8 hrs to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 3/5 1:29 am 36 1.6 117 52.3 2.1 4 mi. ESE of Coso Junction 3/5 5:51 am 34 33.8 116 30.8 2.2 25 mi. ENE of Lucerne Valley 3/5 6:03 am 34 59.3 118 43.4 2.0 12 mi. ENE of Grapevine 3/5 8:50 pm 36 4.0 117 38.6 2.4 17 mi. E of Coso Junction 3/5 9:47 pm 36 4.0 117 38.3 5.2 FELT AT RIDGECREST AND CHINA LAKE 3/5 9:49 pm 36 3.7 117 37.8 4.8 " 3/5 9:50 pm 36 4.1 117 38.1 3.0 " 3/5 9:51 pm 36 4.4 117 38.3 3.7 " 3/5 9:54 pm 36 4.3 117 37.5 4.5 " 3/5 9:55 pm 36 3.9 117 37.6 3.1 " 3/5 9:56 pm 36 5.0 117 37.3 2.7 " 3/5 10:02 pm 36 4.1 117 37.5 2.6 " 3/5 10:03 pm 36 4.2 117 37.7 3.1 " 3/5 10:04 pm 36 4.0 117 37.4 3.1 " 3/5 10:04 pm 36 4.4 117 37.8 2.7 " 3/5 10:05 pm 36 4.9 117 38.8 3.5 " 3/5 10:07 pm 36 4.8 117 37.8 2.6 " 3/5 10:07 pm 36 4.0 117 39.1 2.9 " 3/5 10:08 pm 36 4.9 117 37.9 2.7 " 3/5 10:14 pm 36 3.9 117 38.7 3.2 " 3/5 10:22 pm 36 5.8 117 38.2 2.8 " 3/5 10:23 pm 36 3.3 117 38.5 3.0 " 3/5 10:30 pm 36 4.3 117 37.4 2.7 " 3/5 10:31 pm 36 4.7 117 38.3 3.1 " 3/5 10:43 pm 36 4.5 117 37.8 2.8 " 3/5 10:48 pm 36 4.4 117 37.8 2.8 " 3/5 11:04 pm 36 4.6 117 38.0 2.7 " 3/5 11:21 pm 36 4.4 117 38.4 2.5 " 3/5 11:30 pm 36 4.3 117 38.3 3.3 " 3/5 11:36 pm 36 3.7 117 38.8 4.4 " 3/5 11:43 pm 36 4.2 117 37.8 2.9 " 3/6 12:17 am 36 4.4 117 37.5 3.2 " 3/6 1:16 am 36 4.6 117 37.4 2.6 " 3/6 1:23 am 36 4.1 117 38.1 2.6 " 3/6 1:35 am 36 4.7 117 37.8 2.5 " 3/6 1:48 am 36 4.3 117 38.1 2.6 " 3/6 2:53 am 36 4.7 117 37.2 3.7 " 3/6 2:55 am 36 4.6 117 37.7 3.6 " 3/6 2:56 am 36 5.8 117 37.4 2.5 " 3/6 2:57 am 36 4.5 117 38.0 2.7 " 3/6 3:34 am 36 3.8 117 37.9 2.8 " 3/6 3:52 am 36 5.1 117 37.1 2.5 " 3/6 4:28 am 36 4.5 117 37.3 2.7 " 3/6 5:30 am 36 3.8 117 37.9 3.7 " 3/6 7:56 am 36 4.6 117 37.4 3.2 " 3/6 9:51 am 36 4.6 117 50.2 2.3 6 mi. ENE of Coso Junction 3/6 9:55 am 33 39.5 117 48.8 2.0 Under Irvine 3/6 11:53 am 36 3.4 117 38.7 2.7 17 mi. E of Coso Junction 3/6 2:00 pm 36 5.3 117 37.2 2.6 " 3/6 4:01 pm 36 4.2 117 37.8 3.1 " 3/6 4:36 pm 36 4.6 117 37.1 5.0 FELT AT RIDGECREST AND CHINA LAKE 3/6 4:37 pm 36 4.4 117 37.4 4.8 " 3/6 4:42 pm 36 4.7 117 37.5 2.9 " 3/6 4:43 pm 36 5.2 117 37.7 2.5 " 3/6 4:46 pm 36 4.4 117 37.4 2.6 " 3/6 4:50 pm 36 5.8 117 37.5 2.6 " 3/6 4:50 pm 36 4.7 117 37.5 2.8 " 3/6 4:50 pm 36 4.5 117 37.7 2.7 " 3/6 4:53 pm 36 5.4 117 37.3 2.7 " 3/6 5:02 pm 36 5.2 117 37.5 2.5 " 3/6 5:53 pm 36 4.8 117 37.5 2.8 " 3/6 7:31 pm 36 4.4 117 37.4 3.2 " 3/6 7:33 pm 36 3.6 117 38.5 3.3 " 3/6 8:37 pm 36 4.7 117 37.5 2.8 " 3/6 10:32 pm 34 40.1 119 28.5 2.2 18 mi. N of Carpinteria 3/6 10:45 pm 36 0.7 117 47.2 2.2 9 mi. ESE of Coso Junction 3/6 10:53 pm 36 4.3 117 37.5 2.5 17 mi. E of Coso Junction 3/7 12:59 am 34 21.1 116 28.1 2.1 16 mi. N of Yucca Valley 3/7 3:53 am 35 43.0 118 3.0 2.2 23 mi. SSW of Coso Junction 3/7 4:03 am 36 4.4 117 37.4 2.7 17 mi. E of Coso Junction 3/7 4:42 am 36 4.6 117 37.2 3.0 " 3/7 4:45 am 36 4.1 117 37.3 2.5 " 3/7 6:34 am 36 4.6 117 37.8 2.5 " 3/7 8:03 am 36 4.7 117 37.0 2.6 " 3/7 12:04 pm 34 34.2 116 17.7 2.3 29 mi. N of Joshua Tree 3/7 12:21 pm 36 3.8 117 38.6 2.5 17 mi. E of Coso Junction 3/7 4:31 pm 36 4.8 117 37.5 2.5 " 3/7 4:59 pm 36 4.5 117 37.0 2.5 " 3/7 5:47 pm 36 4.2 117 38.2 3.1 " 3/7 6:16 pm 36 5.1 117 38.0 2.6 " 3/7 7:03 pm 36 4.4 117 37.2 3.2 " 3/7 11:57 pm 36 4.2 117 38.0 3.4 " 3/8 12:35 am 33 16.9 115 39.3 2.1 6 mi. SE of Bombay Beach 3/8 1:26 am 33 16.8 115 39.3 2.2 " 3/8 7:28 am 36 4.5 117 37.0 3.9 17 mi. E of Coso Junction 3/8 2:42 pm 35 57.2 117 37.4 2.9 19 mi. NW of Trona 3/8 7:49 pm 35 20.8 118 31.2 2.1 15 mi. NNW of Tehachapi 3/8 10:05 pm 36 4.5 117 36.9 2.5 17 mi. E of Coso Junction 3/8 11:10 pm 34 29.8 116 29.7 2.2 26 mi. N of Yucca Valley 3/8 11:52 pm 33 24.9 116 23.2 2.2 11 mi. N of Borrego Springs 3/9 4:22 am 35 6.3 118 21.0 2.5 5 mi. ESE of Tehachapi 3/9 8:26 pm 33 59.7 116 35.0 2.0 3 mi. S of Morongo Valley 3/10 2:30 am 36 4.7 117 38.0 3.1 17 mi. E of Coso Junction 3/10 6:06 am 33 19.3 116 17.6 2.0 6 mi. NE of Borrego Springs 3/10 7:39 pm 36 4.8 117 37.7 3.0 17 mi. E of Coso Junction 3/11 4:00 am 35 29.4 118 21.4 2.1 11 mi. SSE of town of Lake Isabella 3/11 4:18 am 34 1.4 117 13.8 4.5 2 mi. SE of Loma Linda WIDELY FELT IN INLAND EMPIRE 3/11 5:07 am 36 4.2 117 37.2 2.8 17 mi. E of Coso Junction 3/11 3:05 pm 33 44.9 115 55.2 2.0 15 mi. N of North Shore 3/11 3:05 pm 33 45.0 115 55.3 2.0 " -------------------------------------------------------------